[chrisjp]

Batteries usually expire slowly and when they start to struggle starting the car, it’s definitely time for a nice new one.

My experience with modern batteries is that they sometimes do completely expire overnight, unlike batteries a few years back that gave you warnings by being audibly slower at cranking the engine when starting.
On a previous modern car (not a Jag) I had driven home one evening with everything normal and then next day it wouldn't start and I got the Christmas tree warning lights all over the dashboard. A new battery completely resolved this.

 

[glcohen]

I have had this happen with a nearly new battery and so far have not found the cause - see my post in this section. I have found one rather warm relay which I suspect has some connection to the problem.

 

[JRJHealey]

Little update - the car started just fine after sitting for a week despite giving me the warning again.

The car is going to the garage tomorrow anyway so I'll get them to do some deeper diagnostics at least.

 

[Davejag]

What is the warning you are getting, exactly?

 

[JRJHealey]

It says something along the lines of "Battery low - please start engine" with a red warning triangle and pops up on the little screen between the speedo/rev counter.

 

[bik3rz]

as mentioned numerous of times already...car needs new battery

 

[Davejag]

It says something along the lines of "Battery low - please start engine" with a red warning triangle and pops up on the little screen between the speedo/rev counter.

I know on the XF the BMS will deliberately discharge the battery to go through a self-calibration routine. The procedure can bring up this message and happens every six months. I am not 100% sure with the XE.

 

[JRJHealey]

as mentioned numerous of times already...car needs new battery

Yeah fingers crossed that's all it is.

I know on the XF the BMS will deliberately discharge the battery to go through a self-calibration routine. The procedure can bring up this message and happens every six months. I am not 100% sure with the XE.

I've read about this, but I think it's unlikely given that I've had the car about 2 years now and it's never done it before.

 

[bik3rz]

I know on the XF the BMS will deliberately discharge the battery to go through a self-calibration routine. The procedure can bring up this message and happens every six months. I am not 100% sure with the XE.

never seen that in my 6 years of x250 ownership, 2 years of xe, or nearly a year in x260...

 

[Davejag]

never seen that in my 6 years of x250 ownership, 2 years of xe, or nearly a year in x260...

X250. Principles of Operation. The BMS module measures battery voltage and current which provides information about the battery state of charge (SOC) and state of health (SOH). SOH measurements provide an indication of battery condition. The BMS compares this information to new and used stored battery values. Battery information is then communicated to the rear junction box (RJB) over a LIN bus connection. The RJB transmits the battery information to the instrument cluster via the MS CAN bus. The instrument cluster displays battery charge warning messages to indicate generator or BMS faults. The instrument cluster also acts as a gateway between the MS CAN and HS CAN bus networks to transmit battery condition information to the ECM from other modules (audio and climate control, for example). Based on the information received from the BMS module, the ECM will control the output from the generator via LIN bus. The ECM can also request the switching off or reducing of power to electrical loads if necessary and override the BMS signals if a fault is detected. The BMS also monitors battery status with the engine switched off, sending a signal to switch off the infotainment system if necessary to protect the battery condition. Once triggered, the engine must be run for at least 5 minutes to charge the battery before the infotainment system will be allowed to operate with the engine switched off for a second time. Calibration Periodically the BMS module will instigate a self-calibration routine. To self-calibrate, the BMS first charges the battery to its full condition. Once the battery is fully charged, the BMS will discharge the battery to approximately 75% of its full state of charge, but never lower than 12.2 V. The time taken to complete this part of the routine is dependent on the electrical load on the vehicle and the length of time the vehicle is used. When the second part of the routine has been successfully completed, the BMS will return the battery to its optimum level of charge. The optimum level of charge will be between 12.6 V and 15 V, depending on battery condition, temperature and electrical loading. This process is run approximately twice a year. NOTE: If the vehicle is only driven for short periods the self-calibration and charging process could take a number of days to complete. CAUTION: Due to the self-calibration routine, it is recommended that all power supply diagnostic testing is carried out using IDS rather than a digital multi-meter

 

[bik3rz]

X250. Principles of Operation. The BMS module measures battery voltage and current which provides information about the battery state of charge (SOC) and state of health (SOH). SOH measurements provide an indication of battery condition. The BMS compares this information to new and used stored battery values. Battery information is then communicated to the rear junction box (RJB) over a LIN bus connection. The RJB transmits the battery information to the instrument cluster via the MS CAN bus. The instrument cluster displays battery charge warning messages to indicate generator or BMS faults. The instrument cluster also acts as a gateway between the MS CAN and HS CAN bus networks to transmit battery condition information to the ECM from other modules (audio and climate control, for example). Based on the information received from the BMS module, the ECM will control the output from the generator via LIN bus. The ECM can also request the switching off or reducing of power to electrical loads if necessary and override the BMS signals if a fault is detected. The BMS also monitors battery status with the engine switched off, sending a signal to switch off the infotainment system if necessary to protect the battery condition. Once triggered, the engine must be run for at least 5 minutes to charge the battery before the infotainment system will be allowed to operate with the engine switched off for a second time. Calibration Periodically the BMS module will instigate a self-calibration routine. To self-calibrate, the BMS first charges the battery to its full condition. Once the battery is fully charged, the BMS will discharge the battery to approximately 75% of its full state of charge, but never lower than 12.2 V. The time taken to complete this part of the routine is dependent on the electrical load on the vehicle and the length of time the vehicle is used. When the second part of the routine has been successfully completed, the BMS will return the battery to its optimum level of charge. The optimum level of charge will be between 12.6 V and 15 V, depending on battery condition, temperature and electrical loading. This process is run approximately twice a year. NOTE: If the vehicle is only driven for short periods the self-calibration and charging process could take a number of days to complete. CAUTION: Due to the self-calibration routine, it is recommended that all power supply diagnostic testing is carried out using IDS rather than a digital multi-meter

Meeeh Sure, but never had 'battery low [...]' msg because of that

 

[BOBCDP]

Oh God!! And this of course is progress. Oh for nice round ammeter and oil pressure gauges again

 

[chrisjp]

Oh God!! And this of course is progress. Oh for nice round ammeter and oil pressure gauges again

Absolutely - why do cars have to be SO complicated these days?

 

[Wastegate84]

Because you like options like a heated steering wheel, 825w sound system and electric seats....

 

[chrisjp]

Because you like options like a heated steering wheel, 825w sound system and electric seats....

But these luxuries existed on upmarket cars before the advent of CANBUS systems and multiple control modules for everything, talking to each other over the BUS

 

[Wastegate84]

So you'd be happy if your XE was a few hundred kg heavier due to all the wiring? I think not.

 

[Andrew453]

My 2015 2.0D is still running the original battery with no issues at 60k; the dreaded stop-start even works...assuming I have forgotten to turn the damn thing off. I give it a regen charge on my cetec every couple of months or so and keep expecting to have problems, but no warning lights as yet. I think I will change it before this winter, though.

 

[JRJHealey]

Some slight developments.

The garage had the car in yesterday, and couldn't find any obvious problems. The battery reported good again for them. To confuse matters more, I've had no warnings for the past 2 days, which is about 4 or 5 stops/starts.

I'm getting them to put a new battery on in any event as I guess it can't hurt, particularly with winter on the way.

Perhaps makes me wonder if it was the BMS calibration afterall.

Another of life's mysteries apparently...

 

[glcohen]

I have had this happen with a nearly new battery and so far have not found the cause - see my post in this section. I have found one rather warm relay which I suspect has some connection to the problem.

After much investigation I have solved my "Low Battery" warning problem. It was caused by one failing cell in an 80AH AGM TAB (Volta) battery. What was happening was that if the battery was discharged by just a few % the battery terminal voltage would suddenly drop from over 12v to just over 10v. It would stay stable at that and the car could be used but the warning would persist until the battery was recharged. I had to persuade the battery supplier to do a load test on the battery as when the battery was fully charged the standard voltage test showed it to be OK. A discharge test immediately showed up the failure and they replaced the battery under its warranty.

 

[First Jag-g-g]

Though rare in new batteries, what you experienced does sometimes happen. I'm glad you were able to get it replaced under warranty for free.